We derive a new melting point depression theory based on the extended perturbed hard sphere chain (PHSC) model to interpret phase behaviors of solid polymer electrolyte systems with various salts. Quantitative descriptions according to the proposed model are in good agreement with experimental data for the given systems. The obtained results show that the salt weight fraction and the size of salt molecule play a great role in determining eutectic points of the given systems. (C) 2003 Elsevier Science B.V. All rights reserved.